MMSE RAKE Reception for Asynchronous DS/CDMA Overlay Systems and Frequency-Selective Fading Channels

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In this work the authors introduce and analyze a detection scheme for simultaneous suppression of multiaccess and digital narrowband interference (NBI) for an asynchronous DS/CDMA system operating over a frequency-selective fading channel. The proposed detector may possibly consider a processing interval greater than the bit-interval, and amounts to a RAKE structure, wherein each branch is designed under an MMSE optimization strategy, followed by a proper combining rule. It is shown that narrowband interference rejection entails in general a time-varying detection structure.

As to the performance assessment, we give closed-form formulas for the system Bit Error Rate (BER), Near-Far Resistance and Signal-to-Interference Ratio (SIR). Numerical results show that the proposed receiver proves effective in suppressing interference, and that it largely outperforms conventional multiuser detectors which do not account for the presence of the NBI, at the price of little complexity increase.

Finally, we provide a blind adaptive implementation of the proposed receiver, based on the exponentially weighted Recursive-Least-Squares (RLS) algorithm, and requiring knowledge of the relevant parameters of the desired user only, and of the NBI signaling time.

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